mmc: rename mmc_boot_partition_access() to mmc_host_can_access_boot()

It is not obvious that this functions checks capabilities. Rename it to
include '_can' like other capability helpers and reword it slightly.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250501063325.7262-10-wsa+renesas@sang-engineering.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>